document.write( "Question 393702: 1. At present, the sum of the parent's age is twice the sum of the children's ages. Five years ago, the sum of the parents' ages was 4 times the sum of the children's ages.fifteen years hence, the sum of the parent's ages will be equal to the sum of the children's ages. how many children are there?
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Algebra.Com's Answer #279520 by ankor@dixie-net.com(22740)\"\" \"About 
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At present, the sum of the parent's age is twice the sum of the children's ages.
\n" ); document.write( " Five years ago, the sum of the parents' ages was 4 times the sum of the children's ages.
\n" ); document.write( "fifteen years hence, the sum of the parent's ages will be equal to the sum of the children's ages.
\n" ); document.write( "how many children are there?
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\n" ); document.write( "Let c = sum of the childrens age at present
\n" ); document.write( "Let n = no. of children
\n" ); document.write( "Let p = sum of the parents age at present
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\n" ); document.write( "\"At present, the sum of the parent's age is twice the sum of the children's ages.\"
\n" ); document.write( "p = 2c
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\n" ); document.write( "\" Five years ago, the sum of the parents' ages was 4 times the sum of the children's ages.
\n" ); document.write( "p-10 = 4(c-5n); (we have to subtract 5 yrs for each person)
\n" ); document.write( "p-10 = 4c - 20n
\n" ); document.write( "Replace p with 2c
\n" ); document.write( "2c - 10 = 4c - 20n
\n" ); document.write( "2c - 4c + 20n = 10
\n" ); document.write( "-2c + 20n = 10
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\n" ); document.write( "\"fifteen years hence, the sum of the parent's ages will be equal to the sum of the children's ages.\"
\n" ); document.write( "p + 30 = c + 15n; (we have to add 15 yrs for each person)
\n" ); document.write( "Replace p with 2c
\n" ); document.write( "2c + 30 = c + 15n
\n" ); document.write( "2c - c - 15n = -30
\n" ); document.write( "c - 15n = -30
\n" ); document.write( "Multiply the above equation by 2, add to the previous equation
\n" ); document.write( "2c - 30n = -60
\n" ); document.write( "-2c +20n = 10
\n" ); document.write( "-----------------adding eliminates c, find n
\n" ); document.write( "-10n = -50
\n" ); document.write( "n = +5 children
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\n" ); document.write( "Check this by finding c, using c - 15n = -30
\n" ); document.write( "c - 15(5) = - 30
\n" ); document.write( "c = -30 + 75
\n" ); document.write( "c = 45 is the sum of the childrens age
\n" ); document.write( "then
\n" ); document.write( "p = 2(45)
\n" ); document.write( "p = 90 is sum of the parents age
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\n" ); document.write( "Check solution in the statement:
\n" ); document.write( "\" Five years ago, the sum of the parents' ages was 4 times the sum of the children's ages.
\n" ); document.write( "90 - 10 = 4(45-5(5))
\n" ); document.write( "80 = 4(45-25)
\n" ); document.write( "80 = 4(20)
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\n" ); document.write( "We can say that there are 5 children\r
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